The invention is directed to a container combination for the transportation and storage of irradiated fuel elements of nuclear reactors consisting of a removable inner container which also is usable by itself for the storage in correspondingly laid out fuel element storehouses and an outer container wherein the two containers in each case have their own cover.
The previous practice is to store spent fuel elements in water basins. In this case the water has the task of shielding the radiocative radiation set free in the decay and to reliably transfer to the outside the simultaneously set free heat of decay. In this case there are expensive and costly precautions required to guarantee dependable cooling.
Therefore there was also considered the dry storage of fuel elements. Thus, e.g. it has been proposed to tightly pack spent fuel elements in steel boxes, place the boxes individually in shielded cells in layered shafts and lead off the residual heat of the fuel elements from the surface of the box with ambient air by free convection.
A disadvantage of this conception of storage is that the spent fuel elements must be unloaded at the storage place from the transportation container into the storage boxes. During the unloading the fuel elements are not protected, besides defective fuel rods must be reckoned with so that there is an increased risk of setting free activity and nuclear fuels. Therefore the reload operation must be remotely controlled and take place in a hot cell. The closing of the boxes and the control of the sealing likewise can only be carried out by remote control.
An additional storage concept is described in Boldt U.S. Pat. No. 3,828,197. Here there are stored in the free air containers with high-level radioactive waste in thick walled metal containers having shielding covers. In this case also for unloading the container from the transportation container into the storage shielding a hot cell is required. This concept thus also has the same disadvantage as the previously described concept.
A further concept therefore provides for further storage of the spent fuel elements in the container employed for the transportation. In this case an unloading of the fuel element at the storage place is not required. However, a disadvantage in this container storage is that the costly and expensive transportation container during the entire storage time cannot be employed for further transportation. This storage concept consequently is very capital expensive.
Therefore there have also been described many times two part transporation containers consisting of an outer and an inner container, thus, e.g. in Blum German OS 2147133 a container combination of an inner container with shielding walls and cover for gamma rays and an outer container laid out as a pressure container. The annular gap between outer and inner container is filled with water as a medium for neutron shielding and for heat transfer. This combination container, however, has various disadvantages. Thus, e.g. in the loading in the nuclear power plant the inner container cannot remain in the outer container so that there exists the danger of contamination. Also the handling therefore deviates substantially from the loading of customary transportation containers which leads to difficulties with the loading devices and the loading personnel. The pressure container surrounds the thick walled .gamma. shielding and the neutron shielding. The thick walled gamma shielding does not contribute to the strength but in an accident acts as an additional load factor on the outer container.
Water is necessary for the transfer of heat from the inner container to the outer container. In case of the loss of this water due to an accident the safety of the combination container is no longer guaranteed. There also exists the danger of the formation of radioactive hydrogen.
In inserting the inner container as storage container the entire .gamma. shielding remains on the storage container. This places an additional load on the storage structure and increases the cost of the storage concept.
Likewise in Lindsay U.S. Pat. No. 3,575,601 there is described a combination container consisting of an outer, shock resistant steel container and a plurality of shielding inserts. This container besides the previously described disadvantages has the further disadvantage that the inner insert as storage container additionally must be made tight at all places of connection of the shielding parts. Also in Smith, Jr. U.S. Pat. No. 2,935,616 there is described a multi-part container. It consists of outer shielding segments screwed together and a thin walled inner container. Since the inner container does not have a cover of its own, the insertion as storage container is not possible.
Therefore it was the problem of the present invention to provide a combination container for the transportation and the storage of spent fuel elements from nuclear reactors, consisting of a removable inner container which is also usable for its own in correspondingly laid out fuel element storehouses, and an outer container, whereby both containers in each case has its own cover. This combination container should not have the above described disadvantages, especially the inner container should make possible a dry storage of spent fuel elememts without changing the fuel elements at the storage place in a storage box and without unnecessary squandoring of space and weight load.